Hi,all chickens have coccidiosis in their gut,there are 4 different types of coccidiosis.It becomes a problem when it multiplies to excess,then it makes the chicks or adults ill.
You need to decrease the chances of it multiplying,it does this in damp ground or bedding around water containers,and,in dirty areas where there are a lot of droppings.
I would introduce your new chick when you have to,just keep the brooder spotless,and move food and water containers to different area's.
The treatment that I used,told me to wash the brooder/hen house with the water that had the treatment in it that hadn't been drunk daily.This said it would kill the coccidiosis bacteria.